1. Technical Field
The present disclosure relates to an energy harvesting device and to a method of forming such a device. In particular, the present disclosure relates to a device that converts thermal energy into electrical energy.
2. Discussion of the Related Art
It has been proposed to use a bimetal plate, which changes shape under varying temperature conditions, in combination with a layer of piezoelectric material, to convert thermal energy into electrical energy.
FIG. 1 substantially reproduces FIG. 2 of U.S. patent application 2011/083714. As illustrated, a curved bimetal plate 100 comprises a support layer 102, which changes shape in response to temperature variations. Plate 100 is shown having a first shape in the form of an arch, and for example changes shape to the form of an inverted arch when its temperature changes. A layer 104 of piezoelectric material is superposed over the support layer 102. A piezoelectric material is one that has the property of generating a voltage difference between its main surfaces that varies depending on the stress applied to it. During a shape change of the curved metal plate 100, a stress S occurs in the piezoelectric layer 104, represented by arrows in FIG. 1, resulting in variations in the voltage signals V− and V+ present on the top and bottom surfaces of the piezoelectric layer 104. The curved metal plate 100 is, for example, positioned in a cavity between hot and cold walls, such that its middle section contacts with the hot and cold walls when the curved plate 100 assumes its respective shapes. This results in a periodic shape change of the metal plate 100, leading to the generation of a periodic voltage signal from which electrical energy can be extracted.
There is a need in the art for a simple and low cost energy harvester that operates based on the above principles and that can provide an efficient conversion of thermal to electrical energy in a range of different environments.